Measuring apparatus for timber grinding mills

ABSTRACT

Apparatus for measuring the amount of wood pulp processed by a timber grinding machine, including a motor driven log grinder and log feeder, and a counter for measuring the energy output of the grinder and feeder motors as an indication of the quantity of wood processed. A blocking circuit coupled to the motors disables the counter when the speed of the motors increases rapidly due to the emptying of the feeding mechanism.

Sandblom Sept. 9, 1975 [54] MEASURING APPARATUS FOR TIMBER 2,902,651 9/1959 Friedrichs 324 110 GRINDING MILLS 3,092,337 6/1963 Patterson 241/34 3,117,734 1/1964 McCarty et a1 241/34 X [75] Inventor: Henry Sandblom, Vasteras, Sweden 3 04 4 9 1971 Keycs ct a1, 241/36 [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden i [22] Filed: July 5, 1973 Primary Examiner-Eugene G. B012 [2]] Appl- 9 376,294 Attorney, Agent, or FirmKenyon & Kenyon Reilly Related US. Application Data Carr & Chapin [63] Continuation of Ser. No. 782,802, Dec. 11, 1968,

abandonedv 57 AB T T [30] Foreign Application Priority Data 1 s RAC Dec. 19, 1967 Sweden 17383/67 Apparatus for measuring the amount of wood pulp processed by a timber grinding machine, including a [52] US. Cl. 235/151.1; 241/35; 318/39; motor driven 10g grinder and log feeder, and a counter 2 73/133 R for measuring the energy output of the grinder and [51] hit. Cl. B02C 19/20; 1302C 25/00 feeder motors as an indication of the quantity of Wood 158] of Search 324/177 H0; 235/92 processed. A blocking circuit coupled to the motors 235/92 151-1; 241/34 37; disables the counter when the speed of the motors in- 318/39; 73/133; 317/19 creases rapidly due to the emptying of the feeding mechanism. [56] References Cited UNITED STATES PATENTS 5 Claims, 12 Drawing Figures 1,871,499 8/1932 Crago 318/39 CONVERTER Cumes/v'r 27 PaTfiNrlo/wrr TRANsFORMER @l-GCK/NG c/Rcu/r VOLTAGE TRANSFORMER ,1 39 4M 1- 1 E Z g/6NAER/ L. I m M/Tr i En o/sce/M INA 10E auLA a 27 5 CONVERTEP PATEN IEH SEP 9 i975 Fig. 7 8

Fig. 9 3 @l #30 Fig. 70

' 7 M Fig. 2 fi 38 {I720 A? 3-4 39/ 40 Fig. 7/

INVEN TOR. HENRY SANDBLOM MEASURING APPARATUS FOR TIMBER GRINDING MILLS This is a continuation, of application Ser. No. 782,802, filed Dec. ll, I968 now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to the control of grinding machines having at least one grinding member and at least one feeding member, each having its own driving motor.

In many industries, including the pulp industry, it is necessary to be able to measure specific energy consumption. One example of this is in the wood pulp industry, in which it is necessary to measure the grinding energy consumed per quantity of wood fed to a grinding mill. The quantity of wood fed into a grinding mill is normally calculated from the movement of an element of the feeding mechanism, such as a chain in the case of a chain grinding mill. There are other types of grinding mills using different methods for feeding the wood which require that other factors be considered in the calculations. However, in all these methods the measurement is affected by such variables as the density of the wood or the material to be ground or machined, the size of the logs, and irregular loading of the logs into the feeding mechanism.

In chain grinding mills, for example, the feeding chains are normally driven by one or more direct current motors. To adjust such a motor to a constant feeding speed, the pole voltage thereof is regulated, which is usually a measurement of the feeding speed. This signal has a low signal to noise ratio. If this combined voltage curve is studied, a certain fundamental curve shape is found for normal grinding upon which noise is superimposed. The curve has sharp high peaks which occur when the space above the grinding stone of the mill is empty. The feeding speed then increases towards its maximum and a voltage peak occurs until wood is again pressed against the stone. Corresponding to this, at the driving motor for the grinding stone rapid fall-off of power or torque also occurs.

SUMMARY OF THE INVENTION The invention seeks to utilize these conditions to obtain accurate measurement of signals for the quantity of wood fed, the grinding energy used per quantity unit fed, etc. The invention is characterized in that a signal, proportional to the current, power, speed, torque or other value dependent on the load of the grinding or feeding motor is supplied to a signal emitter which emits a digital or analog signal corresponding to the value measured. The signals obtained from the grinding and feeding motors are compared to a reference signal value in order to obtain a difference signal which is supplied to a counter to obtain a measured characteristic value, such as the energy quantity fed per log quantity fed. When the difference signal exceeds a certain reference value, the input signals to the counter are blocked and a correction for uneven feeding is obtained. The output of the counter is, thus, an accurate representation of the feeding rate, that is, the quantity of material per feeding length unit or the like, the quantity of timber or material fed in, number of kWh machining energy/volume unit fed, or whatever else is to be measured in such circumstances. It is thus unnecessary to consider the abovementioned feeding error factors and,

the measured value obtained can instead be used directly.

DESCRIPTION OF THE DRAWINGS In the drawings, wherein similar reference numerals denote similar elements throughout the several views thereof:

FIG. I is a schematic diagram of a measuring system for a timber grinding mill constructed according to the invention;

FIG. 2 is a schematic diagram of another embodiment of a measuring system for a timber grinding mill constructed according to the invention;

FIG. 3 is a schematic diagram of still another embodiment of a measurement system for a timber grinding mill constructed according to the invention;

FIG. 4 is a graphical illustration of the motor voltage of the driving motor of the timber feeding mechanism of the grinding mill; and

FIGS. 5-12 are schematic illustrations of exemplary analog and digital components of the measuring systems of FIGS. 1-3.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. I shows a timber grinding mill including an asynchronous driving motor 11 for driving a grinding stone l2, and two log feeding chains 14 driven by a direct current motor I3. Signals proportional to the voltage and the armature current, respectively, of the motor 11 are generated by means of a voltage transformer I5, and a current transformer I6, respectively, and are fed to an emitter 17 (for example a contact emitter gauge) which emits an analog signal having a magnitude dependent on the power consumption of motor I]. The signal emitted from emitter I7 is combined in a summation device 18 with a first reference voltage signal from a reference potentiometer 18a which is proportional to the power consumption of motor II (normal grinding power) and generates a difference signal E which is transmitted to a power regulator 19 to control the speed of the feeding motor 13. The difference signal has a frequency dependent upon the power consumption of motor 11, and is also used to control a counter 28 which is used for indicating purposes. The differcnce signal is, thus, transmitted to a second summation device 20 in which it is combined with a second reference voltage from another potentiomcter 21, the function of which will now be described with reference to FIG. 4.

FIG. 4 shows the voltage curve of the speed controlled feeding motor 13. When there is no log in contact with the grinding stone 12 a voltage peak 22 occurs, which peak must not be permitted to affect the operation of counter 28. The enabling of the counter should be blocked until the voltage has dropped again. The voltage level at the feeding motor I3 (or the corresponding power consumption of the driving motor 11 at which the counter should be disabled is set by the reference potentiometer 21. In the circuit illustrated in FIG. I the actual deviation from the desired power, i.e., the difference signal, is compared with the highest permissible power at which the enabling counter 28 is to take place, represented by a voltage from reference potentiometer 21, by summation device 20. The output signal of device 20 normally emits a specified signal which is transmitted to a pair of AND gates 24 and 25. When the voltage output of summation device 20 exceeds the permissible difference, theoutput signal from discriminator 23 to the AND gates 24 and 25 is terminated.

An analog signal proportional to the voltage, speed or power of the feeding motor 13 is transmitted by a line 26 to a converter 27 whose output signal comprises a pulse train which has a frequency dependent on the motor voltage, speed or power. This output signal is fed to the AND gate 24 and corresponds to the quantity of wood (uncorrected) fed/time unit.

When no load is on the motor 11 (corresponding to high speed for the motor 13) the output signal from the AND gate 24 is blocked. Under other motor load conditions, the output signal from AND gate 24 is transmitted to, and integrated in, the counter 28 and a signal constituting a corrected measurement of the quantity of wood fed (for example measured in m) is obtained.

A signal corresponding to the actual power is transmitted by line 28 to AND gate 25, and in the same way as in the case of the AND gate 24, this signal is blocked when a peak 22 occurs. The corrected value fed to the counter 28 when the AND gate 25 is unblocked is integrated and thus constitutes a measurement of the grinding energy used (for example kWh). The different signals transmitted to the counter may also be suitably filtered to obtain average value signals.

Thus, from the counter unit 28 output signals can be obtained for the density, corrected quantity of wood, corrected grinding energy per unit quantity of wood, and an alarm signal for abnormal operating conditions, etc., and these output signals can be used for indication, data processing, control, etc. The input signal generated by emitter 17 may also comprise a pulse train having a frequency dependent upon the power consumption of motor I I. In such an embodiment, the output signal generated by power regulator 19 is converted from digital to analog form. The signal output of the potentiometer 18a may be converted in known manner to a pulse train having a specified frequency. When the frequency of the output signal of summation device 18 exceeds that of the output signal of potentiometer 21 (which is also converted to a pulse train in the same manner as potentiometer 18a), blocking is effected.

The embodiment of the invention illustrated in FIG.

2 includes a circuit in which measurement of the power consumed by grinding stone driving motor 29 is carried out by means of a magnetostrictive torque gauge 30 of known type. The output signal (analog) of gauge 30 is combined with a signal which is proportional to the quantity of wood fed in a conventional electronic division circuit 31 consisting of an electronic multiplier and an amplifier. The wood feeding signal is transmitted through a potentiometer 32 to an integrator which calculates the quantity of wood fed per specified time unit, such as m /h. In the integrator a pulse train is obtained with a frequencyff 'V'dl, where V is the armature voltage of the feeding motor. The integrated signal is transmitted through an AND gate 33 with a blocking circuit 52 of the same type as in FIG. 1, to a mean value converter 34 which drives a potentiometer 38 whose output signal is proportional to the quantity of wood fed per time unit, such as m/lz (corrected for no-load). The length of a measuring period is set by means of a time switch 37 and zero-setting pulses are also obtained for renewed measurement.

The signal obtained from the divisional circuit is supplied to an indicating or registering instrument, such as a recorder 36, which indicates the grinding energy consumed in kWh/m of wood fed, and this value is thus corrected for a no-load condition on the grinding motor or at high speed of the feeding motor, respectively.

In the circuit illustrated in FIG. 3 two mean value instruments 39, 40 are used, each having its own potentiometer 41, 42. A signal proportional to the power of the driving motor 53 is obtained through a contact emitter gauge 50 as a pulse train having a frequency proportional to the power. The voltage or speed of the feeding motor 43 is converted (by means of a tachometer-generator, not shown) to a pulse train having a frequency proportional to the feeding rate. The pulses can also be generated directly by a suitable pulse emitter. A measuring device 44 for the voltage of the feeding motor 43 adjusts a potentiometer 45, the output voltage of which is thus proportional to the feeding speed or voltage of motor 43. This output voltage is supplied to an integrator 46 which integrates for a certain time period I, and the output signal from the integrator consists of a pulse train having a frequency proportional to the quantity of wood fed during said time unit I. The latter output signal is supplied to an average value instrument 40 through an AND gate 48 which is blocked when the feeding speed signal (from the potentiometer deviates from a certain reference voltage preset on a reference potentiometer 47. The pulse train from the power signal emitter is supplied to the mean value instrument 39 through an AND gate 49 having the same blocking circuit as the AND gate 48. The output voltages from the potentiometers 41 and 42 are thus proportional to the average of the corrected values for the grinding power kW and the quantity of wood fed per time unit I (MW/ll). The energy used per quantity of wood fed (kWh/m) is calculated in an electronic division circuit 31 (of the same type as the corresponding one in FIG. 2), and this signal together with the signal for nz"//1 (from the potentiometer 42) is sup plied to a recorder 51 or other indicating instrument.

The power emitters 17 in FIG. 1 and 50 in FIG. 3 consist in the most simple case of a motor fed by current and voltage transformers associated with the driving motors 11 and 53, respectively, of the grinding mill. In the analog case, shown in FIGS. 5, 7, 9 and 11, the motor of the emitter controls a potentiometer, the output signal of which is supplied to the simple summation device 18 (FIG. 1) and one of the input terminals of the AND gate 49 (FIG. 3). In the digital case, shown in FIGS. 6, 8, 10 and 12, the same motor can drive a perforated disc, which interrupts a light beam directed towards a photocell. The output signal (to 18 or 49) consists of a pulse train having a frequency depending on the speed of the disc, that is, depending upon the magnitude of the characteristic sensed at the driving motors 11 or 53, respectively. The signals from the summation device 18 are supplied to a power regulator 19 (FIG. 1) which, in the analog case, may consist of an amplifier fed by this input signal and a reference signal (shown in FIG. 7), or in the digital case a digitalanalog converter of conventional type (D/A) and an amplifier unit (as shown in FIG. 8). The output signal of the amplifier is applied to and controls the field of the feeding motor 13. The discriminator 23, shown in detail in FIG. 11, in its most simple form, consists of an amplifier, and when the difference signal exceeds the reference voltage at potentiometer 21 the output signal from the amplifier (in 23) is terminated and no output signal is obtained from the AND gates 24, 25. The signal input to counter 28 comprises a series of pulses (after analog-digital conversion at 27 and corresponding conversion over 28 by converter 27).

In the circuit-illustrated in FIG. 2, the signal from gauge 30 is transmitted to a conventional electronic division circuit 31, which is exemplified in more detail in FIG. 9, consisting of a multiplier (X) and an amplifier 36 in FIG. 2, is a normal recording instrument. The integrator 35, which may comprise a normal integrating amplifier as shown in FIG. 8 (which also corresponds to part 46 in FIG] 3), feeds an AND gate 33 (48), the output signal of which is supplied to an average value converter 34 which is exemplified in FIG 12 as a motor which drives a potentiometer 38. In FIG. 3, similar average value converters are shown at 39 and 40.

In the above described embodiments of the invention, electric signals and apparatus have been used for the various calculations, but it should be noted that, for

example, by pneumatic and hydraulic signals or apparatus, or combinations of these, the calculations can be carried out in some other way, such as in a data machine or the like.

A great number of other embodiments are also feasible within the scope of the following claims.

I claim:

1. Measuring apparatus for wood grinding mills having a grinding member and a feeding mechanism, each driven by individual motors, comprising:

means for measuring a load-dependent characteristic value for each of said motors;

first signal generating means, coupled to said measuring means, for generating first output signals representative of the measured characteristic value of each of said motors;

second signal generating means, coupled to said first signal generating means, and responsive to said first output signals, for generating second output signals representative of a measured value characteristic for said measuring apparatus; and

means, coupled to said first signal generating means,

for blocking transmission of said first output signals to said second signal generating means when said first output signals exceed a predetermined value.

2. The apparatus as recited in claim 1, wherein said second signal generating means comprises a counter.

3. Measuring apparatus for wood grinding mills having a grinding member and a feeding mechanism, each driven by individual motors, comprising:

means for measuring a load-dependent characteristic value for each of said motors;

first signal generating means, coupled to said measuring means, for generating first output signals representative of the measured characteristic value of each of said motors; second signal generating means, coupled to said first signal generating means, and responsive to said first output signals, for generating second output signals representative of a measured value characteristic for said measuring apparatus; and means, coupled to said first signal generating means, for blocking transmission of said first output signals to said second signal generating means when said first output signals exceed a predetermined value;

said first signal generating means including an analog signal emitter, signal summing means coupled to said emitter, a reference potentiometer coupled to said summing means, an amplifier coupled to said summing means and to the feeding motor, and an analog to digital conversion means, coupled to said emitter and to said blocking means.

4. Measuring apparatus for wood grinding mills having a grinding member and a feeding mechanism, each driven by individual motors, comprising:

means for measuring a load-dependent characteristic value for each of said motors;

first signal generating means, coupled to said measuring means, for generating first output signals representative of the measured characteristic value of each of said motors; second signal generating means, coupled to said first signal generating means, and responsive to said first output signals, for generating second output signals representative of a measured value characteristic for said measuring apparatus; and means, coupled to said first signal generating means, for blocking transmission of said first output signals to said second signal generating means when said first output signals exceed a predetermined value;

said blocking means comprising signal summing means, a first reference potentiometer coupled to said summing means, a discriminator coupled to said summing means, and AND logic gate means coupled to said first and second signal generating means.

5. The apparatus as recited in claim 4, wherein said first signal generating means includes an analog to digital converter coupled to the feeding mechanism driving 

1. Measuring apparatus for wood grinding mills having a grinding member and a feeding mechanism, each driven by individual motors, comprising: means for measuring a load-dependent characteristic value for each of said motors; first signal generating means, coupled to said measuring means, for generating first output signals representative of the measured characteristic value of each of said motors; second signal generating means, coupled to said first signal generating means, and responsive to said first output signals, for generating second output signals representative of a measured value characteristic for said measuring apparatus; and means, coupled to said first signal generating means, for blocking transmission of said first output signals to said second signal generating means when said first output signals exceed a predetermined value.
 2. The apparatus as recited in claim 1, wherein said second signal generating means comprises a counter.
 3. Measuring apparatus for wood grinding mills having a grinding member and a feeding mechanism, each driven by individual motors, comprising: means for measuring a load-dependent characteristic value for each of said motors; first signal generating means, coupled to said measuring means, for generating first output signals representative of the measured characteristic value of each of said motors; second signal generating means, coupled to said first signal generating means, and responsive to said first output signals, for generating second output signals representative of a measured value characteristic for said measuring apparatus; and means, coupled to said first signal generating means, for blocking transmission of said first output signals to said second signal generating means when said first output signals exceed a predetermined value; said first signal generating means including an analog signal emitter, signal summing means coupled to said emitter, a reference potentiometer coupled to said summing means, an amplifier coupled to said summing means and to the feeding motor, and an analog to digital conversion means, coupled to said emitter and to said blocking means.
 4. Measuring apparatus for wood grinding mills having a grinding member and a feeding mechanism, each driven by individual motors, comprising: means for measuring a load-dependent characteristic value for each of said motors; first signal generating means, coupled to said measuring means, for generating first output signals representative of the measured characteristic value of each of said motors; second signal generating means, coupled to said first signal generating means, and responsive to said first output signals, for generating second output signals representative of a measured value characteristic for said measuring apparatus; and means, coupled to said first signal generating means, for blocking transmission of said first output signals to said second signal generating means when said first output signals exceed a predetermined value; said blocking means comprising signal summing means, a first reference potentiometer coupled to said summing means, a discriminator coupled to said summing means, and AND logic gate means coupled to said first and second signal generating means.
 5. The apparatus as recited in claim 4, wherein said first signal generating means includes an analog to digital converter coupled to the feeding mechanism driving motor. 